Primordial aqueous alteration recorded in water-soluble organic molecules from the carbonaceous asteroid (162173) Ryugu

We report primordial aqueous alteration signatures in water-soluble organic molecules from the carbonaceous asteroid (162173) Ryugu by the Hayabusa2 spacecraft of JAXA. Newly identified low-molecular-weight hydroxy acids (HO-R-COOH) and dicarboxylic acids (HOOC-R-COOH), such as glycolic acid, lactic acid, glyceric acid, oxalic acid, and succinic acid, are predominant in samples from the two touchdown locations at Ryugu. The quantitative and qualitative profiles for the hydrophilic molecules between the two sampling locations shows similar trends within the order of ppb (parts per billion) to ppm (parts per million). A wide variety of structural isomers, including α- and β-hydroxy acids, are observed among the hydrophilic molecules. We also identify pyruvic acid and dihydroxy and tricarboxylic acids, which are biochemically important intermediates relevant to molecular evolution, such as the primordial TCA (tricarboxylic acid) cycle. Here, we find evidence that the asteroid Ryugu samples underwent substantial aqueous alteration, as revealed by the presence of malonic acid during keto–enol tautomerism in the dicarboxylic acid profile. The comprehensive data suggest the presence of a series for water-soluble organic molecules in the regolith of Ryugu and evidence of signatures in coevolutionary aqueous alteration between water and organics in this carbonaceous asteroid.

Primordial aqueous alteration recorded in water-soluble organic molecules from the carbonaceous asteroid (162173) Ryugu A list of authors and their affiliations appears at the end of the paper We report primordial aqueous alteration signatures in water-soluble organic molecules from the carbonaceous asteroid (162173) Ryugu by the Hayabusa2 spacecraft of JAXA.Newly identified low-molecular-weight hydroxy acids (HO-R-COOH) and dicarboxylic acids (HOOC-R-COOH), such as glycolic acid, lactic acid, glyceric acid, oxalic acid, and succinic acid, are predominant in samples from the two touchdown locations at Ryugu.The quantitative and qualitative profiles for the hydrophilic molecules between the two sampling locations shows similar trends within the order of ppb (parts per billion) to ppm (parts per million).A wide variety of structural isomers, including αand β-hydroxy acids, are observed among the hydrophilic molecules.We also identify pyruvic acid and dihydroxy and tricarboxylic acids, which are biochemically important intermediates relevant to molecular evolution, such as the primordial TCA (tricarboxylic acid) cycle.Here, we find evidence that the asteroid Ryugu samples underwent substantial aqueous alteration, as revealed by the presence of malonic acid during keto-enol tautomerism in the dicarboxylic acid profile.The comprehensive data suggest the presence of a series for watersoluble organic molecules in the regolith of Ryugu and evidence of signatures in coevolutionary aqueous alteration between water and organics in this carbonaceous asteroid.
Pristine samples from the near-Earth asteroid (162173) Ryugu returned to Earth by the Hayabusa2 spacecraft provided a valuable opportunity to reveal the organic astrochemistry preserved for over 4.6 billion years in the Solar System [1][2][3][4] .This unique opportunity for investigating primordial organic molecules illuminates several scientific contexts involving carbonaceous asteroids, including the following questions [5][6][7] : -What is the role of carbonaceous asteroids in the Solar System history?-What are the origins and characteristics of the light elements, e.g., carbon (C), nitrogen (N), hydrogen (H), oxygen (O), and sulfur (S)? -What do their isotopic compositions reveal?-How do they record the primordial organic evolution on the asteroid?
-Is the nature of molecular chirality symmetric or asymmetric?-How do interactions between water, organic matter, and minerals affect chemical diversity?
To address these important scientific questions, the Hayabusa2 soluble organic matter (SOM) team 6 evaluated aggregate fine grain samples from the first and second touchdown sites (hereafter, TD1 and TD2); hence, the bulk chemistry data from these two sample collections are averaged representative values for the surface (A0106) and possibly subsurface (C0107) environments (i.e., TD2 was near the artificial crater, for which the depth was ~1.7 meters below ground level 8 ) of Ryugu (Fig. 1).For further insight at the organic molecular level, the SOM team determined the first answers to these questions based on carbon (C), nitrogen (N), hydrogen (H), oxygen (O), sulfur (S) elements and their isotopic profiles 6,9,10 , monocarboxylic acids 6 , amino acids and their molecular chirality 6,11,12 , pyrimidine nucleobase and N-heterocycles 6,9 , primordial salts and sulfur-bearing labile molecules between the organic and inorganic interfaces 10 , aliphatic hydrocarbons and polycyclic aromatic hydrocarbons (PAHs) 13,14 , comprehensive organic molecular profiles 6,15 , molecular growth signatures 16 , and sub-mm scale spatial imaging for organic homogeneity and heterogeneity in the mineral assemblage 6,17 .According to Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR/MS) analysis, the SOM from Ryugu samples contained highly diverse organic molecules (~20,000 species) in the solvent extracts 6,15 .
Naraoka et al. 6 reported organic molecular diversity from initial bulk (IB) to insoluble organic matter (IOM) in a sequential extraction process using hydrophilic to hydrophobic solvents.In this report, we determine the molecular diversity of polar organic molecules extracted from the first contact between hot water and pristine Ryugu samples and report the unique color characteristics of the sequentially extracted fractions with systematic variations in their 13 C-and 15 N-isotopic profiles.If indigenous water-organic interactions occurred in the history of the asteroid, the signatures of parent body aqueous alteration could have been recorded in these hydrophilic organic molecules (Fig. 2).
To decipher the chemical evolution that occurred in surface and subsurface samples 1,2,18 , we comprehensively evaluated highly diverse hydrophilic organic molecules using capillary electrophoresis (CE) with high-resolution mass spectrometry (HRMS).We used this molecular information to interpret the aqueous alteration processes that asteroid Ryugu has experienced to complement the study by Naraoka et al., who reported organic molecular diversity from initial bulk (IB) to insoluble organic matter (IOM) in the sequential extraction process.

Identification of water-extractable molecules and diverse structural isomers
The Ryugu A0106 and C0107 samples (~10 mg each) were subjected to hot water extraction in sealed ampoules at 105 °C for 20 h for the present study 6 (see Methods).This extraction targeting waterextractable compounds followed previous reports (e.g., hydroxy acids 19,20 ;).We first identified highly diverse hydroxy acids and hydrophilic molecular groups in hot water extracts by CE-HRMS (Fig. 2). Figure 3A shows the baseline resolution of representative hydroxy acids and other molecules from the hot water extracts identified with reference standards (Murchison meteorite; Methods).We determined each molecule by migration time (MT) and the exact mass corresponding to the monoisotopic mass 9 .Short-chain hydroxy acids (e.g., glycolic acid, HO-CH 2 -COOH; lactic acid, CH 3 -CH(OH)-COOH; and glyceric acid, HO-CH 2 -CH(OH)-COOH) were predominant in aggregate samples of A0106 and C0107 from Ryugu (Fig. 3B).
Within the concentration range of 10 ppb to 10 3 ppb [i.e., parts per billion (ppb) as nanograms (ng) hydroxy acid per gram (g) of extracted Ryugu sample] (Table S1), structural isomers of hydroxy acids and molecular abundance were determined.The concentration of lactic acid (C 3 ), which is more abundant than glycolic acid (C 2 ), is consistent with previous reports on the Murchison meteorite 19,20 .Among these homologs of hydroxy acids, we also identified molecules potentially relevant to chemical evolution (e.g., pyruvic acid, C 3 H 4 O 3 ; mevalonic acid, C 6 H 12 O 4 ; and citric acid, C 6 H 8 O 7 ).Since these molecules are important precursors in diverse molecular evolution 21 , demonstrating their presence on the carbonaceous asteroid Ryugu is significant.Specifically, these molecules are biochemically crucial and are intermediate substrates of the lipid synthesis pathway and Krebs cycle.Chemically reactive hydroxy acids (e.g., glycolic acid) may play an important role in molecular evolution for the formation of primary carbon chains 22 .Furthermore, there may be a connection pathway between hydroxy acids and formose reactionderived IOM 23 as side products 24 .
In addition to the previously reported organic acids (e.g., formic acid and acetic acid 6 ) and nitrogen heterocycles 9 , we also identified a new group of diverse carboxylic acids (i.e., monocarboxylic acids for aliphatic, aromatic, unsaturated, and keto acids; Figs. 2, 3 and Tables S1, S2) and nitrogen (N)-bearing molecules, including amines (e.g., urea, CH 4 N 2 O; and glycocyamine, C 3 H 7 N 3 O 2 ), hydroxy-and N-heterocyclic indoles (e.g., dihydroxyindole, C 8 H 7 NO 2 ; and hydroxyindole, C 8 H 7 NO), in hot water extracts.Thus, we suggest that the spectroscopic signals of hydroxyl groups (-OH) and amino/imino groups (-NH) in the infrared spectra (chambers A and C 2 ; A0106 and C0107, 9 ; grain-scale and surface observation; Fig. S13, cf. 17,25:) include a substantial amount of intramolecular -OH and -NH moieties originating from the series of polar organic molecules in the present study.

Aqueous alteration signatures and keto-enol tautomerism
Aliphatic dicarboxylic acids (e.g., C 2 , oxalic acid; C 3 , malonic acid; C 4 , succinic acid; C 5 , glutamic acid; and C 6 , adipic acid) are defined as organic compounds bearing two carboxyl groups (-COOH) with an aliphatic backbone.We detected dicarboxylic acids (e.g., oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, malic acid, and maleic acid) within the concentration range of 10 ppb to 10 3 ppb (Table S1; Fig. 4A).Previous reports have suggested that the relative concentration of malonic acid (HOOC-CH 2 -COOH) in the dicarboxylic acid group is sensitive properties by the process of keto-enol tautomerization 26,27 .Laboratory-based malonic acid formation has been compared with the extraterrestrial origin of dicarboxylic acids from tautomerization 28 .Enol malonic acid is presumed to decompose faster than other dicarboxylic acids because it produces a thermodynamically unstable carbon-carbon double bond (i.e., HO-C = CH-, vinyl alcohol group [29][30][31] ) during aqueous alteration as follows: Hence, the formation of two vinyl alcohol groups on the intramolecular malonic acid is probably more reactive (chemically unstable) than that of other dicarboxylic acids (Fig. 4A, B).After unstable equilibrium is eventually reached under aqueous conditions at higher temperatures 32,33 , keto-enol tautomerism induces decarboxylation to form acetic acid (CH 3 COOH) and carbon dioxide (CO 2 ) as end products (Fig. 4B).Hence, a substantial concentration of acetic acid 6 can result from chemical cleavage of the secondary acetogenic process via malonic acid.Therefore, we suggest that malonic acid (mole%) is a molecular signature of the aqueous alteration process recorded in the asteroid Ryugu.In fact, the relative abundance of malonic acid is an order of magnitude lower than that of CM meteorites (e.g., Murchison and Murray, as shown in Fig. 4A), suggesting a different aqueous history.

The systematics of hydrophilic molecules at two sampling locations on Ryugu
The systematics for elemental and organic chemical surveys, including CNHOS and hydrophilic molecular groups, were compiled to formulate the TD1 and TD2 diagrams (Fig. 5).Within these overviews of surface and potential subsurface sample profiles 1,2,18 , we evaluated Fig. 1 | Profiles of samples obtained from asteroid (162173) Ryugu and various observation photographs from kilometer to micrometer scales.A Ryugu photograph taken with the Optical Navigation Camera Telescopic (ONC-T).The photo was taken on August 31, 2018.Credit: JAXA, Univ.Tokyo etc. B Thermal image of Ryugu from the thermal infrared imager (TIR).The observation indicates that the lowest temperature in the blue section is estimated to be below −50 °C, whereas the lowest temperature in the red section is estimated to be < 60 °C.Please see the onsite data acquisition and temperature dynamics 74,75 .Credit: JAXA etc.The data were collected on August 31, 2018.C The surface of the asteroid Ryugu and the shadow of the Hayabusa2 spacecraft.The image was taken from ONC-W1 at an altitude of 70 m.Date taken: 21 September 2018.D The 1st touchdown operation on Ryugu with CAM-H imaging on 22 February 2019.The image was captured just before touchdown during descent at an altitude of approximately 4.1 m.Credit: JAXA.E Photograph of initial sample A0106 (38.4 mg) 6 from the asteroid Ryugu during the 1st touchdown sampling 1,2 .A photograph of C0107 (37.5 mg) from the 2nd touchdown sampling is shown in Supplementary Fig. S1.The scale bar represents 1 mm (red line).F Reference photograph of the discolored and altered crosssection of the Ryugu sample showing possible precipitates (e.g., C0041) 76 .G The isotopic compositions of C, N, H, and S of the Ryugu aggregate samples for A0106 and C0107 are shown after compilation 6,9,10 .The isotopic compositions of δ 13 C (‰ vs. VPDB), δ 15 N (‰ vs. Air), δD (‰ vs. VSMOW) and δ 34 S (‰ vs. VCDT) are expressed as international standard scales.By comparing the classification of carbonaceous meteorites in the Solar System, the compiled data suggested that the Ryugu sample has isotopic characteristics most similar to the petrologic type of CI chondrite 6,52 .
the average chemical composition and diversity of hydrophilic molecules to determine whether there is potential organic heterogeneity or homogeneity in Ryugu.The total amount of CNHOS light elements (ΣCNHOS) in the IB of A0106 and C0107 were ~21.3 wt% 6 and ~23.7 wt% 9 , respectively (Fig. 5A).Then, ΣCNHOS in the IOM increased by an order of magnitude (Fig. 5B) because the inorganic matrix was eliminated (cf.IOM description 34 ).
To further describe the CI-like organic characteristics, the hydrophilic molecules from Ryugu (A0106 and C0107) were compared to CM-type chondrites from Murchison and Murray (Fig. 6A).According to the composition of amino acids found in the CI-type meteorite Ivuna 39 , the properties of meteoritic amino acids were verified for Ryugu with the same normalization (Fig. 6B).Compared to the CM2 chondrites of Murchison and Murray, CI-type carbonaceous chondrites with parent bodies that have experienced aqueous alteration contain lower total amino acid abundances 39,40 .In this context, Burton and coworkers reported that carbonaceous chondrites that experienced high-temperature thermal alteration along with aqueous alteration (e.g., CI type Y-980115; re-examination with δ 15 N of amino acids 41 ) have much lower amino acid abundances than CI Orgueil and CM Murchison meteorites 40,42 ).Distinct positive correlations were observed in both concentration profiles above the 1:1 line, whereas the principal component-2 (PC2) scores suggested that the concentration of hydrophilic molecules was lower and that the history of aqueous alteration differed between the Ryugu and CM samples (Fig. 6C).Therefore, we suggest that comprehensive surveys of meteoritic amino acids of the CI and CM types are important for classifying Ryugu 6,11,13 .
Stepwise 15 N depletion and 13 C depletion during solvent extractions The mass balance equation 1 for the initial bulk composition of organic matter (normalized to 100% for IB as whole rock) in the Ryugu sample is expressed as the sum of inorganic fractions 10 , soluble and insoluble organic fractions through the following equation: ΣSOM represents the sum of the components extracted in each process of sequential extraction, whereas ΣIOM represents the sum of the insoluble organic fractions, as detailed in previous literature 6,34 .We investigated the nitrogen isotopic profiles during sequential solvent extraction by hot water extracts (#7-1), formic acid extracts (#9), and HCl extracts (#10) for Ryugu (A0106 and C0107) and the CI group reference (Orgueil meteorite 9,10 ) (Fig. 7A).Interestingly, this validation clearly showed that organic solvent extraction resulted in 15 N-enriched profiles (e.g., hot water extracts; < +63.1‰ and < +55.2 ‰ vs. Earth's atmospheric air for A0106 and C0107, respectively) for each extractable organic fraction during the sequential process.Therefore, the nitrogen isotopic composition of the insoluble residue indicated that it B Mechanism underlying keto-enol tautomerism of malonic acid (MA), which converts a chemically stable keto form to an unstable enol-form in the aqueous alteration process.The two enol-forms of the unstable MA tautomer are symmetric and in fact identical molecule.
was conversely depleted of 15 N-organic matter in the stepwise extraction (Fig. 7B).We observed that the carbon isotopic composition of the insoluble residues also tended to be 13 C-depleted down to −17.0 ± 0.2 ‰, as observed for 15 N profiles (down to +28.2 ± 3.8 ‰).This observation (Fig. 7B) agrees well with previous reports on the carbon and nitrogen isotopic compositions of extractable SOM and refractory IOM in Murchison 43 .In contrast, it is interesting to note that the sulfur isotopic composition (δ 34 S) converged to the VCDT scale (~0‰) before and after solvent extraction.Within the SOM fraction, the normalized nitrogen balance of each extract was high in the formic acid fraction, indicating that the pink extracts (A0106 and C0107) contained a substantial amount of hydrophilic organic matter (Supplementary Fig. 5 | Standardization to comparatively verify the elemental and hot waterextractable molecular properties of samples from the 1st touchdown site (TD1) and 2nd touchdown site (TD2) at Ryugu.Notably, the Ryugu sample is of scientific value as a surface (TD1) and subsurface sample (TD2) from the carbonaceous asteroid 1,18 .In this report, we evaluated the hydrophilic organic molecules in surface aggregate (A0106) and subsurface aggregate (C0107) samples as follows.A Light elements in IB samples for total C, N, H, and S and pyrolyzable O in wt%.Compilation after the references 6,9,10 .The error arc indicates the standard deviation (1σ).Here, we define IB as whole-rock bulk, which includes all inorganic matrices such as silicates and carbonates, and IOM as the fraction that does not contain silicates 43 .B CNHOS contents in IOM (sample treatment 34 and measurement by the present report) in wt% (Table S3).C Hydroxy acids, carboxylic acids and other newly identified N-bearing hydrophilic molecules in this study obtained from fraction #7-1 (hot water extracts) in ppb.The molecular assignments and raw data profiles are shown in Fig. 3 and Tables S1, S2, respectively.D Amino acids and amines from fraction #7-1 (hot water extraction) in ppb.The data were compiled after the references 6,11 .Please see the error notation in the diagram 11 .E Major inorganic cations and anions from fraction #7-1 (hot water extracts) on the ppm scale.Please see the report for ammonium ion detection (NH 4 + , ~3 ppm; red diamond symbol) and other important molecules associated with organic and inorganic profiles 10 .The error notations in the diagram indicate 2σ after the reference.F Concentrations of urea and alkyl-urea (i.e., methyl-urea, ethyl-urea, and other alkyl ureas up to C 6urea) were measured in the present study.
Information).Based on the present observations (Fig. 7), the hypothesis regarding isotope fractionation during the formation of meteoritic organic matter 44 , volatile nitrogen molecules and thermally altered N residues in Ryugu 45,46 , and primordial 15 N depletion in the protosolar nebula (down to -400‰) 36 will be important for describing nitrogen dynamics in the Solar System.

Implication of aqueous alteration history on the parent body
When investigating the history of the carbonaceous asteroid (162173) Ryugu, we found definite signatures of aqueous alteration from hydrophilic organic molecules, as shown in the hypothetical concept summary (Fig. 8).We consider that physicochemical and temperature factors (i.e., cold and hot thermal conditions; and icy dry and aqueous wet cycles, Fig. 1B) correlate with the molecular evolution between water and organic matter within the cold hydrothermalism 15 .The coevolutionary outline hypothesized here is also supported by the observations of secondary mineral assemblages and altered vein formations 38,[47][48][49] (Fig. 9).For a comparative investigation of those findings, the origin of Ryugu's water within the history of the parent body will be elucidated in subsequent studies 38,[50][51][52] .As a notable opportunity in 2023, NASA's OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification and Security-Regolith Explorer) spacecraft returned the carbonaceous asteroid (101955) Bennu sample to Earth 53 .We expect that international return missions will offer extremely important scientific opportunities to explore the history of organic chemical evolution.
We hope that the Bennu sample will reveal detailed information on chemical evolution and molecular chirality 6,11,40,54 , including widely diverse hydrophilic molecules in the asteroid history.Notably, the carbonate veins observed on some boulders at Bennu 55 are unique and should reveal interactions between pristine aqueous alteration processes, as discussed in this paper and other perspectives 7,53,56 .Therefore, we conclude here that carbonaceous asteroids are natural laboratories for observing realistic primordial molecular evolution in organic and inorganic contexts.

Sample process and extraction of hydrophilic organic molecules
The description summary of the onsite sample collection from the asteroid Ryugu is reported by the Hayabusa2 International Team 1,2 .To ensure the quality of the pristine sample, the project team performed an environmental evaluation in the prelaunch phase 57,58 , system design and preliminary assessments 59,60 and careful assessment of the sample process during volatile recovery in Australia 61,62 until the curation facility 63,64 .The seamless sample process and the extraction of organic molecules from Ryugu have been described previously 6  S1).B Amino acids for the comparison between CI type (Ivuna) and CM type (Murchison and Murray) based on compilation 39 .Please see the individual molecular information in the diagram with the following review 40 and amino acid profiles for Ivuna and Orgueil (Fig. S14).The error arc indicates the standard deviation (1σ).C Principal component (PC) analysis between Ryugu and CM (Murchison and Murray) regarding hydroxy acids and dicarboxylic and tricarboxylic acids with other hydrophilic molecules based on the panel (A) raw data profile (this study).The PC2 scores between the CM type (Murchison, Murray for sample description 77 ) and CI type of Ryugu (A0106 and C0107; Tables S1, S2) are shown, suggesting a different history of indigenous organic molecules.
(Supplementary Information, Figs.S1-S3).The extracted fractions were photographed (this study; Figs.S5-S8) and analyzed by the SOM team.The insoluble organic residue was processed by the IOM team 34 .

Analysis of hydrophilic molecules for hydroxy acids and mono-, di-, tri-carboxylic acids
We performed capillary electrophoresis-high-resolution mass spectrometry (CE-HRMS) using the ω Scan package (Human Metabolome Technologies, Inc., Japan) as described in previous reports 9,65 .In brief, CE-HRMS analysis was performed with an Agilent 7100 CE capillary electrophoresis system (Agilent Technologies, Inc., Santa Clara, CA, USA) equipped with a Q Exactive Plus (Thermo Fisher Scientific Inc., Waltham, MA, USA), Agilent 1260 isocratic HPLC pump, Agilent G1603A CE-MS adapter kit, and Agilent G1607A CE-ESI-MS sprayer kit (Agilent Technologies, Inc., Santa Clara, CA, USA).The system was controlled with Agilent MassHunter workstation software for LC/MS data acquisition for the 6200 series TOF/6500 series Q-TOF version B.08.00 (Agilent Technologies, Inc., Santa Clara, CA, USA) and Xcalibur (Thermo Fisher Scientific Inc., Waltham, MA, USA).The separation was performed with a fused silica capillary (50 μm i.d.× 80 cm total length) and electrophoresis buffer (H3301-1001, HMT) as the electrolyte.To ensure the accuracy of the analysis, blank measurements were also performed to validate the raw data acquisition.Compound peaks were extracted using MasterHands, and automatic integration software was used to obtain raw signal information, including m/z values, peak areas, and migration times (MTs) 66 .B Carbon, nitrogen, hydrogen, and sulfur profiles (wt%) and their isotopic shifts observed from IB, ΣSOM and ΣIOM.The data were compared with previous references 6,9,10 and this study.The abundance of carbon (wt%), nitrogen (wt%), hydrogen (wt%) and sulfur (wt%) in IOM increased by one order of magnitude because of the dissolution of silicates and other mineral structures.The error arc indicates the standard deviation (1σ).Note the previous reports regarding volatile components 45,46 and inorganic profiles 10,38 .The isotopic profiles of ΣSOM from the sequential extractions are shown in Table S4.Please see the IOM treatment 34 and C-N-S isotopic variations of the Solar System 6,36,79,80 .
We used the most representative carbonaceous meteorite of Murchison 6,9,67 as a reference standard to confirm our qualitative evaluation of the sample matrix effects (Fig. S4).The standard mixture including the working reagents for migration time alignment (e.g., AM1, AM2, AM3, AM4, and AM5) and an internal standard for anion analysis (ISA) were prepared from an HMT metabolomics kit (Human Metabolome Technologies Inc., Tsuruoka, Japan) 65,66,68 .

Tracing CNHSO contents and their isotopic compositions to the IOM fraction
For further isotopic analysis of the organic extracts and IOM residues, we analyzed the elemental abundances of carbon (C, wt%), nitrogen (N, wt%), hydrogen (H, wt%), and sulfur (S, wt%) with isotopic compositions of δ 13 C (‰ vs. VPDB), δ 15 N (‰ vs. Air), δD (‰ vs. VSMOW), and δ 34 S (‰ vs. VCDT), respectively 6,9,10 (Fig. S5).For the total CNS contents and their isotopic compositions (δ 13 C, δ 15 N, δ 34 S), we used an ultrasensitive nano-EA/IRMS method (Flash EA1112 elemental analyzer/Conflo III interface/Delta Plus XP isotope ratio mass spectrometer, Thermo Finnigan Co., Bremen) at JAMSTEC 69,70 (within wide isotopic dynamic ranges in Fig. S10).Analytical validations using the nano-EA/IRMS system were performed during practical analyses and studies on carbonaceous chondrites 41,71 .For the total H and the isotopic compositions (δD), we used a high-sensitive EA/IRMS method (Delta Plus XL isotope ratio mass spectrometer, Thermo Finnigan Co., Bremen) at Kyushu University.The elemental CNH contents (wt%) and their isotopic compositions (δ 13 C-δ 15 N-δD profiles) of Ryugu samples A0106 and C0107 are shown in Fig. 1G based on the compilation 6,9,10 .The δ values of the Ryugu samples for C, N, H and S isotopic compositions are denoted using international isotope standards as follows: with the Vienna Canyon Diablo Troilite (VCDT) standard, respectively.Since the IOM fraction comprises the main portion of various solid organic carbon in Ryugu samples, simultaneous data acquisition for SOM and IOM was performed 6,34 .
Surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) SALDI-MS has been used to analyze many materials, including carbonaceous meteorites 72,73 , at Tohoku University.Briefly, a matrix-assisted laser system (AP-SMALDI5, TransMIT) connected to an orbital trap mass spectrometer (QExactive, Thermo Fisher Scientific Inc., Waltham, MA, USA) was used to acquire SALDI mass spectra.Mass spectrometry was conducted in positive mode with a mass resolution of 140,000 using a solid-state laser of 20 μm, 60 Hz, and 30 pulses for each spot (Fig. S8).Approximately 130 spots in a 300 × 300 μm area in the pit were scanned by the laser.

FTIR spectra and ultraviolet-visible spectra of the organic extracts
We compiled the Fourier transform infrared spectroscopy (FTIR) profiles of the solvent extracts by using a Nicolet iN10 infrared microscope (Thermo Fisher Scientific Inc., Waltham, MA, USA) between A0106 and C0107 (method after the ref. 6).Briefly, 1-2 μL of the solvent extract was dropped onto a BaF 2 plate (1 mm thick) and airdried (Fig. S9).The data acquisition for transmission spectra was performed by an MCT (mercury-cadmium-telluride) detector at liquid N 2 in a clean room at Kyushu University.The microscope and detector were continuously purged with dry N 2 gas during analysis.The ultraviolet-visible (UV-vis) spectra of the extracts were analyzed with a microvolume UV-Vis spectrophotometer (NanoDrop One C, Thermo Fisher Scientific Inc., Waltham, MA, USA) in the wavelength range of 190 nm to 1100 nm (Fig. S7).This spectroscopic measurement was performed at Tohoku University.162173) Ryugu.The left panel represents the initial primary mineral assemblage and fluid veins in the early stage of interaction between water, organics, and rock within the bedrock.The right panel represents altered secondary mineral assemblages (i.e., porous and physically fragile), desiccated veins, and precipitates in the late stage and ongoing stage with dehydration processes at Ryugu 47,50 .Within cold hydrothermalism 15 , thermal history in the asteroid 74,75 , and temperature constraints 38 , this figure conceptualizes aqueous alteration, and the sizes of regolith particles and bedrock are arbitrary scales.Amino acids and other hydrophilic molecules 6 with "salt" formation 10 are overviewed in the illustration diagram of chemical evolution.The organic analysis of the asteroid Bennu 81 is a valuable opportunity to consider the scientific consequences of this study.

Fig. 3 |
Fig. 3 | Representative hydrophilic molecular groups in hydroxy acid, dicarboxylic acid, and tricarboxylic acid in hot water extracts from Ryugu samples (A0106 and C0107) and a reference sample (Murchison).A High-resolution mass electropherogram of capillary electrophoresis during the analysis of hot water extracts (#7-1).The blank was composed of ultrapure water before hot water extraction.Based on the migration time (min) and mass accuracy within ~1 ppm (μg/g) of the theoretical peak (m/z), we assigned each observed peak to the corresponding standard (Fig. S4).B Concentrations of representative hydroxy acids

Fig. 6 |
Fig. 6 | Summary of integrated observations of Ryugu with CI type (Ivuna) and CM type (Murchison and Murray) for aqueous alteration processes throughout their history.A Hydroxy acids, dicarboxylic and tricarboxylic acids, and other newly identified hydrophilic molecules for comparison between Ryugu (this study) and CM (Murchison and Murray; this study) type at the ppb scale.The Ryugu values on the horizontal axis are shown as the average of A0106 and C0107 (TableS1).B Amino acids for the comparison between CI type (Ivuna) and CM type (Murchison and Murray) based on compilation39 .Please see the individual molecular

Fig. 7 |
Fig. 7 | Carbon, nitrogen, hydrogen and sulfur abundances and their isotopic profiles before and after the solvent extraction processes from the organic matter facies.A The 15 N-nitrogen isotopic depletion between the supernatant and IOM residue during sequential solvent extraction for the Ryugu (A0106 and C0107) and Orgueil samples.The pinkish color originates from formic acid extract #9, and the yellowish color originates from HCl extract #10.The other chemical profiles are shown in Figs.S6, S7, and S8.Please also see the residue of IOM (black color) on the bottom of the vial 78 .Unique brownish colloidal-colored fractions (#4 MeOH extract, #5 water extract) were observed for A0106 and C0107 (cf.Figs.S5, S9).

Fig. 8 |
Fig.8| Aqueous alteration of primordial hydrophilic organic molecules and minerals during parent body processing of asteroid (162173) Ryugu.The left panel represents the initial primary mineral assemblage and fluid veins in the early stage of interaction between water, organics, and rock within the bedrock.The right panel represents altered secondary mineral assemblages (i.e., porous and physically fragile), desiccated veins, and precipitates in the late stage and ongoing stage with dehydration processes at Ryugu47,50 .Within cold hydrothermalism15 , https://doi.org/10.1038/s41467-024-49237-6NatureCommunications | (2024) 15:5708Gas chromatography/mass spectrometry (GC/MS) of hexane extracts from the IOM fractionAfter discovering the yellow sticky deposit on the wall in the glass vial containing the IOM fraction (see the pretreatment34 ), we conducted an n-hexane extraction to identify cyclic sulfur molecules (i.e., cyclic hexaatomic sulfur, S 6 ; cyclic heptaatomic sulfur, S 7 ; and cyclic octaatomic sulfur, S 8 ) from the fraction (Figs.S11, S12).We analyzed the extracts by gas chromatography/mass spectrometry (GC/MS; 7890B GC and 5975 C MSD, Agilent Technologies, Inc., Santa Clara, CA, USA) with a VF-5MS column (30 m × 0.25 mm i.d., 0.10 μm film thickness, Agilent Technologies, Inc., Santa Clara, CA, USA) at JAMSTEC.The GC oven temperature was programmed as follows: the temperature was initially 40 °C, ramped up at 30 °C min -1 to 120 °C, ramped up at 6 °C min -1 to 320 °C, and maintained for 20 min.The target molecules were verified by comparison with authentic standards of aliphatic hydrocarbons in n-hexane solution (Supplementary Information) and the library database from NIST (National Institute of Standards and Technology).
numbers; 21KK0062 (Y.T.), 21J00504 (T.K.), 21H04501&21H05414 (Y.O.), 20H00202 J.P.D. and D.P.G. thank NASA for support of the Consortium for Hayabusa2 Analysis of Organic Solubles.This study was conducted in accordance with the Joint Research Promotion Project at the Institute of Low Temperature Science, Hokkaido University (21G008 and 22G008 to Y.T., Y.O., H.N.).